Method and apparatus for allocating paging areas

ABSTRACT

A method for allocating paging areas includes: determining a basic paging area currently visited by a User Equipment (UE); and allocating a paging area to this UE according to a history record of motion trace of UEs located in the basic paging area currently visited by this UE. An apparatus for allocating paging areas is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/538,800, filed on Jun. 29, 2012, which is a continuation of U.S.patent application Ser. No. 13/073,529, filed on Mar. 28, 2011, which isa continuation of International Application No. PCT/CN2009/073906, filedon Sep. 14, 2009, which claims priority to Chinese Patent ApplicationNo. 200810169533.7, filed on Sep. 28, 2008, all of which are herebyincorporated by reference in their entireties.

FIELD

The present disclosure relates to a radio paging technology, and inparticular, to a technology of allocating paging areas.

BACKGROUND

In a wireless communication system, User Equipment (UE) changes to theidle state when no service is active in order to reduce powerconsumption and save radio resources. When the UE is idle, theconnection between the UE and the communication network is released. Ifthe communication network wants to contact the UE, the communicationnetwork needs to page the UE. Multiple wireless coverage areas adjacentto each other are generally designed in a communication system tocontrol overhead of paging messages. When a UE is idle, the scope of thevariable location of the UE tracked by the communication network is awireless coverage area. If the communication network wants to page a UEwhen the UE is in a wireless coverage area, the communication networkneeds only to page the UE within the wireless coverage area that coversthe UE. The wireless coverage area here is called a paging area. Whenthe UE leaves the paging area, the UE needs to notify the communicationnetwork to update the location information of the UE and request thecommunication network to allocate a new paging area.

In practical application, if the paging area is too small, the UE mayleave the current paging area and enters a new paging area frequently inthe motion process, and much location update signaling is generated. Ifthe paging area is too wide, when the communication network pages a UE,the communication needs to send paging messages within a wide scope,which leads to high load of paging. Therefore, in the planning of pagingareas in the deployment of a communication network, a tradeoff betweenthe amount of location update signaling and the paging overhead needs tobe accomplished.

In some communication networks, multiple small wireless coverage areasare planned to control the coverage of the paging area flexibly andavoid change of the wireless configuration parameters, and one or moresmall wireless coverage areas generally combine into a larger wirelesscoverage area which is allocated as a paging area to the UE. The smallwireless coverage areas are called “basic paging areas”. If one pagingarea includes multiple basic paging areas, the UE does not need toinitiate location update to the communication network when the UE movesbetween the basic paging areas. For example, in an Evolved Packet System(EPS), multiple Tracking Areas (TAs) are planned. When allocating pagingareas to the UEs, the EPS may allocate one TA or a larger area composedof multiple TAs to a UE as a paging area based on a certain algorithmaccording to the region, type of the user of the UE, time segment, andother various conditions. A set of TAs included in a paging areaallocated to a UE is called a TA list in the EPS. If a paging areaallocated to the UE includes multiple TAs, the UE does not need toinitiate location update to the EPS when the UE moves between the TAs.

In the prior art, communication technicians perform on-site survey,analyze the adjacent basic paging areas to be potentially visited by theUE after the UE moves to a basic paging area, and then configure thisbasic paging area and the adjacent basic paging areas to be visitedpotentially as a TA list into the communication network. When thecommunication network allocates a paging area to a UE located in thisbasic paging area, the communication network allocates the configured TAlist corresponding to this basic paging area to the UE.

SUMMARY

The embodiments of the present invention provide a method and anapparatus for allocating paging areas in order to allocate paging areasflexibly and appropriately.

A method for allocating paging areas includes: determining a basicpaging area currently visited by a UE; and allocating a paging area tothis UE according to a history record of motion trace of UEs located inthe basic paging area currently visited by this UE.

An apparatus for allocating paging areas includes: a determining unit,adapted to determine a basic paging area currently visited by a UE; anda paging area allocating unit, adapted to allocate a paging area to thisUE according to a history record of motion trace of UEs located in thebasic paging area determined by the determining unit.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the technical solution under the present invention or theprior art more clearly, the following outlines the accompanying drawingsinvolved in description of the embodiments of the present invention orthe prior art. Apparently, the accompanying drawings outlined below areillustrative rather than exhaustive. Persons of ordinary skill in theart can derive other drawings from such accompanying drawings withoutany creative effort.

FIG. 1 is a flowchart of a method for allocating paging areas in anembodiment of the present invention;

FIG. 2 shows a structure of an apparatus for allocating paging areas inan embodiment of the present invention;

FIG. 3 shows an application scenario of a first embodiment of presentinvention;

FIG. 4 is a method flowchart of a first embodiment of the presentinvention;

FIG. 5 shows an application scenario of a second embodiment of presentinvention;

FIG. 6 is a method flowchart of a second embodiment of the presentinvention;

FIG. 7 is a method flowchart of a third embodiment of the presentinvention;

FIG. 8 is a method flowchart of a fourth embodiment of the presentinvention; and

FIG. 9 is a method flowchart of a fifth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description is given in conjunction with theaccompanying drawings in order to provide a thorough understanding ofthe present invention. Evidently, the drawings and the detaileddescription are merely representative of particular embodiments of thepresent invention, and the embodiments are illustrative in nature ratherthan exhaustive. All other embodiments, which can be derived by thoseskilled in the art from the embodiments given herein without anycreative effort, shall fall within the scope of the present invention.

As shown in FIG. 1, a method for allocating paging areas in anembodiment of the present invention includes the following steps:

Step S101: Determine a basic paging area currently visited by a UE.

Step S102: Allocate a paging area to the UE according to a historyrecord of motion trace of UEs located in the basic paging area currentlyvisited by the UE.

Specifically, the basic paging area currently visited by the UE isdetermined according to an identifier (ID) of the currently visitedbasic paging area, where the ID is reported by the UE or a Radio AccessNetwork (RAN).

An operation that accompanies the step of determining the basic pagingarea currently visited by the UE may be: determining at least one basicpaging area visited by the UE before the UE enters the currently visitedbasic paging area, for example, determining a first basic paging areawhich is last visited by the UE before the UE enters the currentlyvisited basic paging area, a second basic paging area which is lastvisited by the UE before the UE enters the first basic paging area, andso on. In this way, a paging area can be allocated to a UE according toa history record of continuous motion trace of multiple UEs located inthe basic paging area currently visited by the UE, where the motiontrace of the UEs is a trace of the UEs moving from at least one basicpaging area previously visited by the UEs to the basic paging areacurrently visited by the UE and to the basic paging areas subsequentlyvisited by the UEs. A paging area allocated to a UE includes at leastthe basic paging area currently visited by the UE, and may include atleast one basic paging area that tends to be visited by the UEs afterthe UEs move from the previous motion trace recorded in the historyrecord to the basic paging area currently visited by the UE. Besides,the at least one basic paging area visited by the UEs before the UEsenter the currently visited basic paging area may be determinedaccording to the ID of at least one basic paging area visited by the UEsbefore the UEs enter the currently visited basic paging area, where theID is reported by the UEs. If the ID of the at least one basic pagingarea previously visited by the UEs is the ID of one basic paging area,the ID of one basic paging area is the ID of the first basic paging arealast visited by the UEs before the UEs move to the currently visitedbasic paging area. Based on the history record of continuous motiontrace of multiple UEs moving from the previously visited basic pagingarea to the currently visited basic paging area and to the subsequentlyvisited basic paging areas, the prediction about the potential trace ofa UE with the same history trace is more accurate, and more appropriatepaging area is generated for the UE.

The contents of the history record depend on the actual needs so long asthe history record reflects the motion trace of multiple UEs. Forexample, the history record may include information indicating how manytimes the UEs in the currently visited basic paging area move to otherbasic paging areas in each unit of time within a specific period. Thehistory record may include: actual number of motions of the UEs from thebasic paging area currently visited by the UE to the basic paging areasadjacent to the currently visited basic paging area, or a resultobtained after the actual number of motions is divided or multiplied bya scale factor. More specifically, if the scale factor is less than 1,the actual number of motions corresponding to the adjacent basic pagingareas inside the paging area is divided by the scale factor, where thepaging area is allocated to the UEs located in the currently visitedbasic paging area or the actual number of motions corresponding to theadjacent basic paging areas outside the paging area is multiplied by thescale factor, where the paging area is allocated to the UEs located inthe currently visited basic paging area.

The motion trace of the UEs in the history record may be motion trace ofmultiple UEs. In practice, however, it is appropriate to record themotion trace of the UEs with a sampling flag. In the statistic period,the paging area allocated to the sampled UEs may include only the basicpaging area currently visited by the sampled UEs in order to obtain dataof continuous motion of the sampled UEs between basic paging areas.

The history record may be a combination of multiple history records,each being maintained in a different time segment.

If the UE is static or moves only in the currently visited basic pagingarea in a specific time segment such as a time length of periodiclocation update, the ID of the at least one basic paging area visitedpreviously may be the ID of the currently visited basic paging area.

If the history record shows that the UEs located in the currentlyvisited basic paging area will most probably stay inside the currentlyvisited basic paging area subsequently, the paging area allocated to theUE may include fewer basic paging areas, for example, include only thebasic paging area currently visited by the UE. Further, the paging areaallocated to the UE may include the basic paging area which will be mostprobably visited by the UEs located in the basic paging area currentlyvisited by the UE among the basic paging areas adjacent to the currentlyvisited basic paging area. The number of basic paging areas included inthe paging area allocated to the UE located in the currently visitedbasic paging area is less than the number of basic paging areas includedin the paging area allocated to the UE located in a different basicpaging area which will be most probably visited by the UE.

Besides, the number of basic paging areas included in the paging areaallocated to the UE depends on at least one of these factors: timesegment, user type, user property, property of the basic paging area,and motion speed of the UE.

The paging area allocated to the UE may include multiple continuousadjacent basic paging areas. The multiple continuous adjacent basicpaging areas are a result of prediction performed according to thehistory record and the trace of motion of the UE between the multiplecontinuous adjacent basic paging areas. In the history record, the UElocated in a basic paging area on the motion trace will more probablymove to the next adjacent basic paging area on the motion trace thanmove to other basic paging areas. In the history record, after the UEmoves from a previous adjacent basic paging area to a basic paging areaon the motion trace, the UE will more probably move from this basicpaging area to the next adjacent basic paging area on the motion tracethan move to other basic paging areas.

The number of multiple continuous basic paging areas on the motion tracedepends on at least one of these factors: user type, property of basicpaging area, time segment, and motion speed of the UE.

The paging area may be allocated to the UE according to presetparameters. The preset parameters may be: an upper threshold of basicpaging areas included in a paging area; or a threshold of a sum ofprobabilities of the UEs moving from the currently visited basic pagingarea to all adjacent basic paging areas in the paging area; or both ofthem.

A recent motion frequency corresponding to a specific paging areaincluded in the paging area allocated to a UE may reach or exceed apreset threshold of the recent motion frequency. The recent motionfrequency corresponding to a specific basic paging area refers to howmany times a UE moves from a currently visited basic paging area to thespecific basic paging area in a recent period; or refers to how manytimes a UE, which has moved from a previous basic paging area to thecurrently visited basic paging area, moves to the specific basic pagingarea in a recent period.

The steps in the foregoing method embodiment and the step of generatingand maintaining the history record may be implemented by the samenetwork entity; or, the steps in the foregoing method embodiment areimplemented by one network entity, and the step of generating andmaintaining the history record is implemented by another network entity.For example, supposing that the previous method embodiment is applied toan EPS, a Mobility Management Entity (MME) may be responsible fordetermining the basic paging area currently visited by the UE,allocating a paging area to the UE, and generating and maintaining thehistory record; or, an MME is responsible for determining the basicpaging area currently visited by the UE and allocating a paging area tothe UE, and a central node is responsible for generating and maintainingthe history record. One or more MMEs may report the motion trace of theUE to the central node, and the central node creates or updates therecord according to the reported motion trace. As required by the MME,or when decided as necessary by the central node, or upon expiry of theset period, the central node may submit the result of analyzing thehistory record to the MME. The motion trace reported by the MME to thecentral node may be statistic data in a specific period. The centralnode may inform the MME of the paging area corresponding to the basicpaging area, for example, when the MME is restarted but the MME storesno history record of motion of the UE. Further, the central node mayanalyze the statistic data reported by the MME, obtain the updatedpaging area corresponding to the basic paging area, and submit theanalysis result to the MME periodically. When the MME needs to allocatea paging area corresponding to a basic paging area to the UE, the MMEmay allocate the paging area submitted by the central node to the UEdirectly.

The foregoing method embodiment may be implemented by differentapparatuses. As shown in FIG. 2, one of the apparatuses for allocatingpaging areas includes:

a determining unit 201, adapted to determine a basic paging areacurrently visited by a UE; and

a paging area allocating unit 202, adapted to allocate a paging area tothis UE according to a history record of motion trace of UEs located inthe basic paging area determined by the determining unit 201.

Specifically, the determining unit 201 may determine the basic pagingarea currently visited by the UE according to the ID of the currentlyvisited basic paging area, where the ID is reported by the UE or RAN.

At the same time of determining the basic paging area currently visitedby the UE, the determining unit 201 may determine at least one basicpaging area visited by the UE before the UE enters the currently visitedbasic paging area, for example, determine a first basic paging areawhich is last visited by the UE before the UE enters the currentlyvisited basic paging area, a second basic paging area which is lastvisited by the UE before the UE enters the first basic paging area, andso on. In this way, the paging area allocating unit 202 can allocate apaging area to a UE according to a history record of continuous motiontrace of multiple UEs located in the basic paging area currently visitedby the UE, where the motion trace of the UEs is a trace of the UEsmoving from at least one basic paging area previously visited by the UEsto the basic paging area currently visited by the UE and to at least onebasic paging area subsequently visited by the UEs. A paging areaallocated to a UE includes at least the basic paging area currentlyvisited by the UE, and may include at least one basic paging area thattends to be visited by the UEs after the UEs move from the previousmotion trace recorded in the history record to the basic paging areacurrently visited by the UE. Also, the determining unit 201 maydetermine at least one basic paging area visited by the UEs before theUEs enter the currently visited basic paging area according to the ID ofat least one basic paging area visited by the UEs before the UEs enterthe currently visited basic paging area, where the ID is reported by theUEs.

The motion trace of the UEs in the history record may be motion trace ofmultiple UEs. In practice, however, it is appropriate to record themotion trace of the UEs with a sampling flag. During the samplingoperation for the motion of a UE, the paging area allocated by thepaging area allocating unit 202 to the sampled UEs includes only thebasic paging area currently visited by the sampled UEs in order toobtain data of continuous motion of the sampled UEs between basic pagingareas.

If the history record shows that the UEs located in the currentlyvisited basic paging area will most probably move inside the currentlyvisited basic paging area subsequently, the paging area allocated by thepaging area allocating unit 202 to the UE may include fewer basic pagingareas, for example, include only the basic paging area currently visitedby the UE. Further, the paging area allocated to the UE may include thebasic paging area which will be most probably visited by the UEs locatedin the basic paging area currently visited by the UE among the basicpaging areas adjacent to the currently visited basic paging area.

The units in the foregoing apparatus may be set as or applied in the MMEof the EPS, and the working mode of such units in the MME is the same asthe working mode in the foregoing apparatus.

To help those skilled in the art better understand the presentinvention, the following gives several embodiments of the presentinvention. In the following embodiments, the network environment is anEPS, “TA” is the basic paging area mentioned above, and “TA list” is thepaging area allocated to the UE.

FIG. 3 shows an application scenario of a first embodiment of presentinvention. In this embodiment, TA1, TA2, and TA4 are adjacent to eachother; TA1, TA2, and TA3 are adjacent to each other; and TA3 is adjacentto TA5.

As shown in FIG. 4, the method in the first embodiment includes thefollowing steps:

Step S401: The MME receives a Tracking Area Update (TAU) Request messagethat carries a Last TAI and a Current TAI. The Last TAI (also known asLast Visited TAI) is an ID of the last TA visited by the UE before theUE enters the current TA; and the Current TAI is an ID of the TAcurrently visited by the UE.

Step S402: The MME locates the record in Table 1 by using the Last TAIin the TAU Request message as a source TA and using the Current TAI as atarget TA. If no record is found, the MME creates the record. If therecord is found successfully, the MME modifies the count field in therecord. As a way of modifying the count field, the MME may add 1 to thecounter, or perform a weighting operation according to the property ofthe user of the UE, target TA, and time segment, namely, add a weightedvalue to the existing count. For example, for a TAU initiated by a VIPuser, the count increases by 1.2; for a TAU initiated by an ordinaryuser, the count increases by 1; for a TAU initiated in rush hours, thecount increases by 1.2; for a TAU initiated in ordinary time segments,the count increases by 1.

TABLE 1 Recent motion Is target Count frequency TA in after a (number ofcurrent scale times per Source Target preferred factor (0.6) Percentsecond, last 10 TA TA Count TA list? is applied Percent order minutes)TA1 TA1 500 Yes 500 51.0% 1 7.9 TA1 TA2 50 No 30  3.1% 4 2.0 TA1 TA3 300Yes 300 30.6% 2 5.3 TA1 TA4 150 Yes 150 15.3% 3 2.5 TA3 TA1 700 Yes 700  35% 1 8.3 TA3 TA2 200 Yes 200   10% 4 3.0 TA3 TA3 650 Yes 650 32.5% 25.1 TA3 TA5 450 Yes 450 22.5% 3 3.5

As shown in Table 1, a record includes these fields: Source TA, TargetTA, Count, Is target TA in current preferred TA List, Count after ascale factor is applied, Percent, Percent order, and Recent motionfrequency. Each record uses the source TA plus the target TA as anindex. “Count” measures how many times a UE or UEs move from the sourceTA to the target TA within the current statistic period. “Is target TAin current preferred TA list” indicates whether the TA list allocated tothe UE includes the target TA when the MME allocates the TA list to theUE in the source TA after analyzing the data in the history record. Inpractice, the MME may analyze the latest data in the history record atintervals such as 10 minutes, and update the TA included in the TA listfor a source TA. “Count after a scale factor is applied” will beinterpreted below. “Percent” is a ratio of a first count to a secondcount, where the first count is a result of multiplying a scale factorby each record in a set of records with the same source TA value inTable 1, and the second count is a total count of multiplying the scalefactor by all records in the set of records. “Recent motion frequency”refers to the number of motions of the UE from the source TA to thetarget TA within a recent period, and is measured in number of times persecond. The statistic period of “Recent motion frequency” is notnecessarily equal to, but may be shorter than, the statistic period ofthe number of motions from the source TA to the target TA.

Table 1 is only an example. In practice, the content of the tabledepends on the actual needs. For example, “Count” does not necessarilycoexist with “Count after a scale factor is applied”.

The MME calculates and refreshes the percent of motions from a source TAto each target TA in real time or periodically, and ranks the motionsaccording to the percent. The percent in the statistics reflects theprobability of the UE moving from a source TA to each target TA. The MMEmay also calculate the frequency of moving from the source TA to thetarget TA recently (such as in the last 10 minutes).

Taking the first four records in Table 1 as an example, the MME receivesand counts 1000 TAU Request messages in which the Last TAI is the ID ofTA1. In such TAU Request messages, there are 500 TAU Request messages inwhich the target TA is still TA1, ranking number 1; there are 300 TAURequest messages in which the target TA is TA3, ranking number 2; thereare 150 TAU Request messages in which the target TA is TA4, rankingnumber 3; and there are 50 TAU Request messages in which the target TAis TA2, ranking number 4.

Nevertheless, the four records do not mean that the adjacent TAs of TA1are TA2, TA3 and TA4 only. TA1 may have other adjacent TAs, but nomotion of the UE from TA1 to the adjacent TA has been statisticized forreasons such as communication lines, and the MME keeps no record ofmotion from TA1 to the adjacent TAs.

It should be noted that the TA currently visited by the UE isnecessarily included in the allocated TA list. In this way, when the MMEranks the records in percentage, the MME does not necessarily calculateor rank the percents for the records whose target TA is the source TA,but calculates and ranks the records in percentage, where target TA inthe record is not the source TA.

Step S403 occurs after step S402: After receiving a new Attach Requestmessage or TAU Request message from a UE, the MME finds a TA to whichthe UE will most probably move from the TA identified by the Current TAIcarried in the message, adds the found TA into the TA list, andallocates the TA list to the UE that sends the message. It should benoted that at the time of allocating a TA list to the UE, the CurrentTAI corresponds to the source TA in Table 1 so that it is practicable todetermine the TA or TAs to which the UE will most probably move.

Supposing that the Current TAI carried in the Attach Request or TAURequest is the ID of TA1, according to the percent order in Table 1, theMME determines the order of probabilities of being the next TA to bevisited by the UE in TA1, and the order from high probability to lowprobability is: TA1->TA3->TA4->TA2.

The following two parameters may be configured on the MME:

(a) upper threshold of the number of TAs in a TA list

For example, it is stipulated that a TA list can include three TAs atmost. If the Current TAI carried in the Attach Request or TAU Request isthe ID of TA1, according to the records in Table 1 and the threshold,the MME determines that the TA list allocated to the UE includes TA1,TA3, and TA4.

(b) threshold of the sum of probabilities of the UEs moving from thecurrent TA to all TAs in the TA list

For example, the set threshold is 80%. If the Current TAI carried in theAttach Request or TAU Request is the ID of TA1, according to the recordsin Table 1 and the threshold, the MME determines that the sum of theprobabilities of moving from TA1 to TA1, TA3, and TA4 is 81.6%, which isgreater than 80%. Therefore, the TA list allocated to the UE includesTA1 and TA3.

When the MME allocates a TA list to the UE, (a) and/or (b) above servesas constraint conditions of the allocation.

The values of parameters (a) and (b) above are determined according tothe actual needs. Specifically, the values of such parameters depend onthe user type, TA, time segment, and property or feature of a singleuser. Here are several examples of setting the parameters:

For the UE that involves few calls and short messages, the maximumnumber of TAs allowed in a TA list may be a large value, and the primarypurpose is to control the amount of location update signaling;

for the UE that moves along a road, the maximum number of TAs allowed ina TA list may be a large value, and the primary purpose is to controlthe amount of location update signaling;

in rush hours, the maximum number of TAs allowed in a TA list may be alarge value, and the primary purpose is to control the amount oflocation update signaling; and

for the UE that moves at a high speed, the maximum number of TAs allowedin a TA list may be a large value, and the primary purpose is to controlthe amount of location update signaling. The MME may judge the motionspeed of the UE according to the frequency of the UE sending ordinaryTAU Request messages (namely, not the TAU Request messages sentperiodically) continuously in a unit of time. For example, the UE sendsan ordinary TAU Request message 4 times per hour, which is greater thanthe threshold 3 times per hour; but the maximum number of TAs allowed ina TA list for this UE is 6, and therefore, the MME increases the maximumnumber of TAs allowed in the TA list allocated to the UE, namely,modifies the threshold to 7.

It should be noted that: If the Current TAI carried in the AttachRequest or TAU Request is the ID of TA1 and the MME determines that theUE will most probably move from TA1 to TA3 and TA4, the MME always letsthe TA list include TA3 and TA4 when the UE initiates the TAU by usingTA1 as the current TA. No TAU is initiated (except periodical TAU) whenthe UE moves between TAs in the TA list. Therefore, the number of sentTAU Request messages will be relatively small when the UE moves from TA1to TA3 and TA4 subsequently. In this way, the percent of the UE movingto the less probable TA (such as TA2) will rise relatively. After awhile, it is possible that the percent of motion from TA1 to TA2 rankshigher, and the MME determines that the UE will more probably move fromTA1 to TA2 than TA4. The percent of motion to TA4 ranks thirdpreviously. When the UE initiates TAU by using TA1 as the current TA,the MME may add TA2 into the TA list. In fact, the number of TAU Requestmessages between TA3 and TA4 will decrease. That is, the number of TAURequest messages between all adjacent TAs in the TA list will decrease.In other words, the percent order of the frequency of moving from a TAto other TAs may be unstable.

For such problems, two corrective solutions are put forward herein:

(u) A “recent motion frequency” field is introduced in Table 1. The“recent motion frequency” refers to frequency of moving from one TA toanother in a recent period. A threshold of the recent motion frequencymay be set. The MME adds the target TA corresponding to the recentmotion frequency into the current preferred TA list only if a recentmotion frequency reaches or exceeds the threshold. For example, it isassumed that the threshold is 3 times per second and the Current TAIcarried in the Attach Request or TAU Request is the ID of TA1. When theMME allocates the TA list to the UE, because the UE in TA1 moves to TA1and TA3 at a frequency of more than 3 times per second in the recentperiod, but the UE moves to TA2 and TA4 at a frequency of less than 3times per second in the recent period, the MME adds TA1 and TA3 into theTA list, but does not add TA2 or TA4 into the TA list. Further, if arecent motion frequency is less than the threshold, the MME may ignorethe record of the recent motion frequency in calculating or ranking thepercent.

After a target TA is added into the preferred TA list of a source TA,the record of motion from the source TA to the target TA is no longerrestricted by the motion frequency threshold. That is, when the MMEfinds that the recent motion frequency of moving from the source TA tothe target TA is less than the threshold, the MME does not exclude thetarget TA from the preferred TA list, but still applies the target TA incalculating and ranking the percent, and the target TA may be rankedlast and excluded from the preferred TA list of the source TA. In thiscase, the record of motion from the source TA to the target TA isrestricted by the recent motion frequency again.

The statistic period of the recent motion frequency may be short, andmay be different from the refresh period of other data in the record.

(v) At the time of ranking the percents, for the records whose target TAis outside the current preferred TA list corresponding to the source TA,the value of the “count” field may be multiplied by a scale factor p,and then the percent is calculated and ranked together with otherrecords. The scale factor p may be obtained in this way: In the samecomparable statistic period, after a target TA is added into a TA list,the MME calculates the ratio of the “number of TAU Request messages fromthe source TA corresponding to the TA list to the target TA” to thenumber counted before the target TA is added into the TA list, and theratio is the scale factor p. The scale factor p may be configuredempirically, and adjusted and optimized on an ongoing basis. In Table 1,the scale factor p is 0.6 fixedly. Nevertheless, the scale factor p maybe generated dynamically according to the statistic result on the MME.The scale factor p may be a globally uniform value, or a value thatvaries with region, time segment, source TA, and target TA.

Nevertheless, if the count corresponding to the target TA not added intothe TA list is not multiplied by the scale factor p, the countcorresponding to the target TA added into the TA list may be divided bythe scale factor p.

Besides, solution (u) and solution (v) may be applied simultaneously orseparately.

According to the protocol, if an idle UE does not move out of thecurrent paging area within a specific time segment and a location updateprocedure is triggered, the UE needs to initiate a special locationupdate procedure, namely, periodical location update procedure, tonotify the current location of the UE to the network and keepsynchronization between the UE and the network. In an EPS, theperiodical location update procedure is a periodical TAU procedure. Ifthe MME finds that the UE in a source TA moves to the source TA at ahigher percent according to the TAU Request messages sent by the UE, itindicates that the users in the source TA primarily stay static or movewithin the source TA, for example, within a residential area or officepremises. In this way, the MME may allocate a TA list that includesfewer TAs to the UE in such a TA in order to save overhead. Suchstatistic characteristics may vary with time. For example, the statisticcharacteristics of a TA in rush hours are different from those inordinary time segments.

In the prior art, the Last TAI is defined as the TA visited by the UEbefore the UE enters the current TA, and always different from thecurrent TA. Therefore, the MME is unable to know whether the UE stays onthe current TA in a long time according to the periodical route updatemessage. In order to optimize the allocation of the TA list when the UEis static, the embodiments of the present invention put forward a methodfor setting Last TAI. For example, when the UE confirms that the UE hasstayed in a TA for a period longer than a threshold, the UE sets theLast TAI to the ID of the current TA when initiating periodical routeupdate. Specifically, the Last TAI may be set in the following way:

The UE sets the stored Last TAI value to the ID of the TA currentlyvisited by the UE at the time of getting attached;

The UE updates the Last TAI to the ID of the current TA when the UEmoves from the current TA to another TA;

The UE sets the stored Last TAI value to the ID of the current TAwhenever the UE performs the periodical TAU; or the UE sets the Last TAIto the ID of the current TA only if the UE does not move from thecurrent TA to another TA within N continuous times of periodical TAU,where the value of N may be configured on the UE or delivered from thenetwork.

In the TAU Request message sent in the TAU procedure, the UE always setsthe Last TAI in the message to the Last TAI value currently stored bythe UE.

When the probability of multiple UEs in a TA moving to the TA reaches orexceeds a preset threshold, the MME determines that the UE generallykeeps static within this TA (for example, the TA covers officepremises). Therefore, the MME may decrease the TAs included in the TAlist appropriately when allocating a TA list to the UE in this TA.

To further optimize the process of generating the TA list, the MME mayperform forward search in the history record of the motion trace of theUE. Specifically, in the history record, if the subsequent motion traceof the UE in the current TA passes through multiple continuous adjacentTAs, the paging area allocated to the UE includes the multiplecontinuous adjacent TAs corresponding to the motion trace. For example,according to the four records in Table 1, the MME determines that no UEhas moved from TA1 to TA5 directly so far because TA1 is not adjacent toTA5 or because the probability of the UE moving from TA1 to TA5 directlyis very low for certain reasons although they are adjacent to eachother. It is assumed that, according to filtering conditions, the MMEdecides to add TA3 into the TA list whose current TA is TA1, butaccording to the last four records in Table 1, the MME determines thatthe UE in TA3 will more probably move to TA5, and therefore, the MMEalso adds TA5 into the TA list. In this way, if the MME moves from TA1to TA3, and then moves from TA3 to TA5, the MME will initiate no TAU,thus saving the signaling. Here, TA1, TA3 and TA5 are called “threecontinuous adjacent TAs”.

Supposing that the UE is currently located in TA1, the approximateprobability of the UE moving from TA1 to TA2, TA3 . . . TA_(N-1), andfinally to TA_(N) is:P _(N) =P _(1#2) *P _(2#3) * . . . *P _(N-2#N-1) *P _(N-1#N)

In the formula above, P_(M#N) is a ratio of the count of motions fromTA_(M) to TA_(N) in Table 1 to the total count of motions from TA_(M) toall adjacent TAs.

The depth of the forward search performed by the MME is generally 1-5.Specifically, the depth can be configured according to the type of user,TA, time segment, and motion speed of the UE. Generally, a greater depthof forward search may be applied to the UE that moves quickly. Forexample, the current ordinary TAU frequency counted for a UE is 4 timesper hour, which exceeds the frequency threshold 3 times per hour; andthe forward search depth set for the UE is 3. Therefore, the MME mayincrease the forward search depth of the UE by 1, and to 4.

In the forward search process, the search depth is limited to themaximum number of TAs included in the TA list allocated to the UE.Meanwhile, for every step of search on the path of forward search,adding a new adjacent TA into the TA list is controlled by a minimumvalue of the sum of probabilities of moving from the current TA to anadjacent TA in every step of search, where the adjacent TA is a TAadjacent to the current TA in the newly accessed TA list. That is, theminimum value of the sum of probabilities is applicable to every step ofsearch. The sum of probabilities may vary with the search depth. Forexample, in a forward search from TA1 currently visited by the UE, inthe first step of search, the adjacent TAs whose motion probability isnot less than 80% are added into the TA list. Supposing that TA3 and TA4are added into the TA list, the next step of search is performed for oneof the motion traces (such as TA3), and the adjacent TAs whose motionprobability is not less than 70% are added into the TA list.

The MME may perform forward search for multiple possible subsequentmotion traces of the UE according to the information in the historyrecord. For example, in the foregoing search process, search may beperformed along two paths: TA1->TA3, and TA1->TA4.

In certain circumstances, several TAs may form a loop. On this loop, theMME may return to the start point after performing forward search forseveral times. Therefore, the MME should check whether suchcircumstances occur on a path in the forward search, and terminate theforward search on the path once they occur.

In this embodiment, step S401 and step S402 deal with the method ofmaintaining the history record of the motion trace of the UE accordingto the information in the TAU Request message; step S403 deals with themethod of allocating a TA list to the UE currently located in a TAaccording to the maintained history record. In fact, step S401, stepS402, and step S403 are not totally separated from each other. Inpractice, when the MME receives a TAU Request message in step S401 andstep S402, a TA list needs to be allocated to the UE according to themaintained history record; when the MME allocates a TA list to a UE instep S403, the MME also maintains and updates the history record of themotion trace of the UE according to the Last TAI and Current TAI in theTAU Request message. Step S401 and S402 are one aspect of the procedure,and step S403 is the other aspect of the same procedure. In thisembodiment, the three steps are described separately in order to makethe description concise.

It should be noted that the MME may maintain the history record in thesame way. Specifically, the MME uses a certain proportion of the UEs assamples randomly. For each sampled UE, the MME always puts only the TAcurrently visited by the sampled UE into the corresponding TA list inthe sampling process. More specifically, in the sampling process, theMME puts only the TA currently visited by a sampled UE into the TA listallocated to the sampled UE whenever the MME allocates a TA list to thesampled UE. All the sampled UEs initiate a TAU procedure whenever theymove out of the current TA. The MME may record the continuous trace ofmotion of the sampled UEs between the TAs. For example, when a UE entersTA1, the MME determines the UE as a sampled UE randomly, and the TA listallocated to the sampled UE includes only TA1. After the sampled UEmoves from TA1 to TA2, the sampled UE sends a TAU Request message thatcarries a Last TAI and a Current TAI, where the Last TAI is the ID ofTA1, and the Current TAI is the ID of TA2. The MME determines that thesampled UE has moved from TA1 to TA2 according to the TAU Requestmessage reported by the UE.

In practice, the MME may maintain different motion trace history recordtables for different time segments. For example, the MME maintain ahistory record for each of these time segments: 7:00-9:00 a.m. (punch-inrush hours), 9:00-15:00 (usual time), and 17:00-19:00 (punch-out rushhours); or the MME maintains a history record for each of these days:Monday to Friday (working days), and Saturday and Sunday (weekends); orthe MME combines such history records when allocating a TA list to theUE, namely, allocates a TA list to the UE according to the combinedhistory record.

As mentioned above, the MME may report the statistic information to acentral node, and the central node analyzes the data and delivers thepreferred TA list of each current TA to the MME in different scenarios(such as different time segments and different user types). The centralnode may obtain statistic information from multiple MMEs, analyze themtogether, and delivers the analysis result to each MME. The analysismethod employed the central node is the same as the analysis methodemployed the MME in this embodiment. In the embodiments to be describedbelow, the central node may also be used to put data together, analyzethe data, and deliver the analysis result, which will not be repeatedany further.

The following describes the second embodiment.

FIG. 5 shows the application scenario of the second embodiment.Supposing that the lines in the illustration indicate roads, the linefrom TA2 to TA3 is one branch of the road, and the line from TA2 to TA4is the other branch. As shown in FIG. 5, if the vehicles from TA3 or TA4to TA2 need to move further, the vehicles can only travel along the roadto TA1 (supposing that the traffic rule does not allow a vehicle toswerve to TA4 at the intersection after the vehicle travels from TA3 toTA2, and does not allow a vehicle to swerve to TA3 at the intersectionafter the vehicle travels from TA4 to TA2). If a vehicle that travelsfrom TA1 to TA2 needs to run further, the vehicle may enter TA3 or TA4.If the method in the first embodiment is applied, the statistic resultshows that the UE moves from TA2 to these TAs most frequently: TA1, TA3,and TA4. Therefore, when the TA currently visited by the UE is TA2, theMME puts TA1, TA2, TA3, and TA4 into the TA list allocated to the UE. Infact, if the UE moves from TA3 into TA2, because it is probable that theUE will enter TA 1 and it is scarcely possible that the UE will swerveto TA4 or turn back to TA3, futile paging overhead will occur if TA3 orTA4 is still included in the TA list in such circumstances.

As revealed in FIG. 5, the UE moving from which TA into the current TAis a factor for deciding the target TA to which the UE will most likelyenter. Considering such a factor, this embodiment puts forward thefollowing two solutions:

(x) When the UE sends a TAU Request message, the TAU Request messagecarries a Last TAI and a Last2 TAI. The Last2 TAI is the ID of the TAvisited by the UE before the UE enters the TA corresponding to the LastTAI, namely, the Last2 TAI indicates the TA from which the UE enters theTA corresponding to the Last TAI.

(y) The MME uses a certain proportion of the UEs as samples randomly.For each sampled UE, the MME always puts only the TA currently visitedby the sampled UE into the corresponding TA list in the samplingprocess. More specifically, in the sampling process, the MME puts onlythe TA currently visited by a sampled UE into the TA list allocated tothe sampled UE whenever the MME allocates a TA list to the sampled UE.All the sampled UEs initiate a TAU procedure whenever they move out ofthe current TA. The MME may record the continuous trace of motion of thesampled UEs between the TAs. For example, when a sampled UE enters TA1,the TA list allocated by the MME to the sampled UE includes only TA1.After the sampled UE moves from TA1 to TA2, the sampled UE sends a TAURequest message that carries a Last TAI and a Current TAI, where theLast TAI is the ID of TA1, and the Current TAI is the ID of TA2. The TAlist reallocated by the MME to the sampled UE includes only TA2. Afterthe sampled UE moves from TA2 to TA3, the sampled UE sends a TAU Requestmessage that carries a Last TAI and a Current TAI again, where the LastTAI is the ID of TA2, and the Current TAI is the ID of TA3. According tothe motion trace of the UE between the TAs, the MME determines that thesampled UE has moved to TA3 after the sampled UE moves from TA1 to TA2.

Solution (1) brings the same effect as solution (2) above.

The second embodiment is based on solution (x), and solution (y) will bedetailed in the fifth embodiment later.

As shown in FIG. 6, the method in the second embodiment includes thefollowing steps:

Step S601: The MME receives a TAU Request message. The TAU Requestmessage carries Last TAI, Last2 TAI, and Current TAI. The meanings ofLast TAI, Last2 TAI, and Current TAI have been described above.

Step S602: The MME locates the record in Table 1 by using the Last2 TAIin the TAU Request message as a source TA, using the Last TAI as anintermediate TA, and using the Current TAI as a target TA. If no recordis found, the MME creates the record. If the record is foundsuccessfully, the MME modifies the count field in the record. As a wayof modifying the count field, the MME may add 1 to the counter, orperform a weighting operation according to the property of the user ofthe UE, target TA, and time segment, namely, add a weighted value to theexisting count.

TABLE 2 Recent motion Is frequency target Count (number TA in after a oftimes current scale per preferred factor second, Source IntermediateTarget TA (0.6) is Percent last 10 TA TA TA Count list? applied Percentorder minutes) TA1 TA2 TA1 10 No  6 NA*1 NA 0.5 TA1 TA2 TA2 40 NA NANA*2 NA 2.1 TA1 TA2 TA3 850 Yes 850 93.4%  1 10 TA1 TA2 TA4 100 No  60 6.6% 2 5.7 TA3 TA2 TA2 100 NA NA NA*2 NA 2.5 TA3 TA2 TA1 1400 Yes 1400 100% 1 15.4 TA2 TA3 TA3 300 NA NA NA*2 NA 6.4 TA2 TA3 TA5 700 Yes 700100% 1 12.5 *1In this record, because the recent motion frequency islower than the threshold, it is excluded from the factors forcalculating and ranking the percents in this embodiment. *2In thisembodiment, the records whose target TA is the current TA are notinvolved in calculating or ranking the percents.

The MME calculates and refreshes the percent of motions from the samesource TA and intermediate TA to each target TA in real time orperiodically, and ranks the motions according to the percent.

Taking the first four records in Table 2 as an example, the MME receivesand counts 1000 TAU Request messages, in which the Last2 TAI is the IDof TA1 and the Last TAI is the ID of TA2. In such messages, there are 10TAU Request messages in which the target TA is still TA1; there are 40TAU Request messages in which the target TA is TA2; the TAU Requestmessages using TA3 as the target TA are more than the TAU Requestmessages using TA4 as the target TA. That is, among the UEs that movesfrom TA1 to TA2, a majority of them enter TA3, and a minority of thementer TA4.

The fifth record and the sixth record in Table 2 are statistics of 1500TAU Request messages in which the Last2 TAI is the ID of TA3, and theLast TAI is the ID of TA2.

The last two records in Table 2 are statistics of 1000 TAU Requestmessages, in which the Last2 TAI is the ID of TA2 and the Last TAI isthe ID of TA3. It should be noted that after the UE moves from TA2 toTA3, the counted frequency of the UEs moving to TA3 is relatively high.One possible reason is that: A rest area exists in TA3, and the vehiclethat carries UE stays in the rest area for a long time, and multipleperiodical TAU procedures occur in TA3.

Table 2 is only an example. In practice, the content of the tabledepends on the actual needs. For example, “Count” does not necessarilycoexist with “Count after a scale factor is applied”.

Step S603 occurs after step S602: After receiving a new Attach Requestmessage or TAU Request message from a UE, the MME allocates the TA listcorresponding to the Current TAI and the Last TAI to the UE that sendsthe message according to the Current TAI and Last TAI carried in themessage and the maintained record. It should be noted that at the timeof allocating a TA list to the UE, the Current TAI corresponds to theintermediate TA in Table 2 and the Last TAI corresponds to the source TAin Table 2 so that it is practicable to determine the TA or TAs to whichthe UE will most probably move.

Supposing that the Last TAI carried in the Attach Request message or TAURequest message is the ID of TA1 and the Current TAI carried in themessage is the ID of TA2, according to the records in Table 2, the MMEdetermines the order of probabilities of being the next TA to be visitedby the UE after the UE moves from TA1 to TA2, and the order from highprobability to low probability is: TA3->TA4. The records correspondingto TA1 and TA2 are not involved in the ranking of probabilities. TA1 isnot involved in the ranking because it does not fulfill the stipulatedrecent motion frequency threshold; TA2 is not involved in the rankingbecause it must be included in the TA list. The operation method in thisembodiment does not allow such records to participate in the calculationof ranking.

Like the first embodiment, the following three parameters may beconfigured on the MME:

(a) upper threshold of the number of TAs in a TA list

(b) threshold of the sum of probabilities of the UEs moving from thecurrent TA to all TAs in the TA list

(c) threshold of recent motion frequency

When the MME allocates a TA list to the UE, (a), or (b), or (c) above orany combination thereof serves as constraint conditions of theallocation.

Solution (u) and solution (v) in the first embodiment above are alsoapplicable to the second embodiment.

For the fourth record in Table 2, if TA4 is not included in the currentpreferred TA list allocated to the UEs which move from TA1 to TA2, thestatistics show that there are 100 occasions of the UEs moving to TA4among the UEs which have moved from TA1 to TA2, but the 100 occasionsare multiplied by a scale factor 0.6 to obtain only 60 occasions. The 60occasions and the 850 occasions counted in the third record areincorporated in the calculation and ranking of the percents.

In the second embodiment, “Is target TA in current preferred TA list”indicates whether the TA list allocated to the UE includes the target TAwhen the MME allocates the TA list to the UE which moves from a specificsource to another specific intermediate TA after the data in the historyrecord is analyzed. In practice, the MME may analyze the latest data inthe history record at intervals such as 10 minutes, and update the TAincluded in the TA list for a source TA and a specific intermediate TA.

According to Table 2, among the UEs which have moved from TA1 to TA2,the MME calculates the weighted probabilities of the UEs moving to thetarget TA, and the order from high probability to low probability isTA3(93.4%)->TA4 (6.6%). If the configured threshold is 90%, the MME mayadd only TA3 and TA2 into the TA list; if the configured threshold is95%, the MME adds TA3, TA4, and TA2 into the TA list.

In order to optimize the allocation of the TA list to the static UEs, amethod for setting Last TAI and Last2 TAI is put forward. The settingmethod enables the MME to determine the relative static state of the UE.The TA list allocated to a relatively static UE may include fewer TAs.Specifically, the Last TAI and Last2 TAI may be set in the followingway:

When getting attached, the UE sets the stored Last TAI value and Last2TAI value to the ID of the TA currently visited by the UE;

When moving from the current TA to another TA, the UE updates the storedLast2 TAI value to the stored Last TAI value, and then updates thestored Last TAI value to the ID of the current TA newly visited by theUE;

While M procedures of TAU occur continuously at intervals, if the TAcurrently visited by the UE keeps unchanged, the UE sets the Last2 TAIvalue to the Last TAI value; while N procedures of TAU occurcontinuously at intervals, if the TA currently visited by the UE keepsunchanged, the UE sets the Last TAI value to the Current TAI value,where M and N may be configured on the UE or delivered by the network.The M counter and the N counter are cleared to 0 only when the currentTA of the UE changes; when the M counter and the N counter are bothgreater than or equal to the set value, the Last TAI and Last2 TAI needsto be updated. As regards whether the Last TAI is updated first or theLast2 TAI is updated first, it depends on the policy on the UE. Forexample, while Max(M,N) procedures of TAU occur continuously atintervals, if the TA currently visited by the UE keeps unchanged, theLast2 TAI value, the Last TAI value and the Current TAI value carried inthe TAU Request message are the same, namely, they are the ID of the TAcurrently visited by the UE.

According to the statistics, if the MME finds that the UE which hasmoved from a source TA to an intermediate TA will more probably move tothe intermediate TA than other TAs, and, if the probability reaches orexceeds a threshold, the MME determines that the UEs in the intermediateTA generally keep static or move inside the intermediate TA. Therefore,the MME can reduce the TAs included in the TA list to save the pagingoverhead. It should be noted that: After the UE in the intermediate TAkeeps static for a period, the source TA may the intermediate TA.

The forward search described in the first embodiment above is alsoapplicable to the second embodiment. For example, supposing that a UE iscurrently located in TA2, the MME determines that the UE will probablymove to TA3 after the UE moves from TA1 to TA2 according to Table 2, andtherefore, the MME adds TA3 into the TA list. Through forward search inTable 2, the MME determines that the UE will more probably move to TA5after the UE moves from TA2 to TA3, and therefore, the MME adds TA5 intothe TA list. For the UE that moves quickly, a greater depth of forwardsearch may be applied.

It should be noted that the MME may maintain the history record in thesame way. Specifically, the MME uses a certain proportion of the UEs assamples randomly. For each sampled UE, the MME always puts only the TAcurrently visited by the sampled UE into the corresponding TA list inthe sampling process. More specifically, in the sampling process, theMME puts only the TA currently visited by a sampled UE into the TA listallocated to the sampled UE whenever the MME allocates a TA list to thesampled UE. All the sampled UEs initiate a TAU procedure whenever theymove out of the current TA. The MME may record the continuous trace ofmotion of the sampled UEs between the TAs. For example, when a UE entersTA1, the MME determines the UE as a sampled UE randomly, and the TA listallocated to the sampled UE includes only TA1. After the sampled UEmoves from TA1 to TA2, the sampled UE sends a TAU Request message thatcarries a Last TAI and a Current TAI, where the Last TAI is the ID ofTA1, and the Current TAI is the ID of TA2. The TA list reallocated bythe MME to the sampled UE includes only TA2. After the sampled UE movesfrom TA2 to TA3, the sampled UE sends a TAU Request message that carriesa Last TAI and a Current TAI again, where the Last TAI is the ID of TA2,and the Current TAI is the ID of TA3. According to the continuous motiontrace of the UE between the TAs, the MME determines that the sampled UEhas moved to TA3 after the sampled UE moves from TA1 to TA2.

The first embodiment and the second embodiment describe how the MMEdetermines the times that the UE moves between TAs according to all TAURequest messages, and analyze an incidental phenomenon: After severalTAs are added into the TA list corresponding to a specific TA, the TAUprocedures between two adjacent TAs in such TAs decrease. Such aphenomenon exerts only a slight impact on the ranking stability of fewtarget TAs to which the UE will less probably move from the specific TA.Moreover, the impact may be overcome through method (u) and method (v)described in the first embodiment and the second embodiment, withoutaffecting the practicability of the method for collecting statistics inthe first embodiment and the second embodiment. Another method forcollecting statistics is put forward herein: The MME counts the timesthat the UE moves between TAs through sampling. With enough samples,this method for collecting statistics reflects the probability of the UEmoving between adjacent TAs accurately, without generating theincidental phenomenon mentioned in the first embodiment and the secondembodiment.

Therefore, a third embodiment is described below. In the thirdembodiment, the MME allocates a TA list inclusive of only one TA to thesampled UE selected randomly, and obtains the number of motions of thesampled UEs between two adjacent TAs. As shown in FIG. 7, the method inthis embodiment includes the following steps:

Step S701: The MME receives an Attach Request message or TAU Requestmessage. The Attach Request message or TAU Request message carries aCurrent TAI. The TAU Request message further carries a Last TAI.

Step S702: If a TAU procedure is initiated by the UE, the MME judgeswhether a sampling flag is set in the context of the UE. If a samplingflag is set in the UE context, the MME determines that the UE contextstored on the MME already stores the TAI corresponding to the TA visitedby the UE in the previous attaching or TAU procedure of the UE. This TAIis called a Previous TAI. The Last TAI carried in the TAU Requestmessage sent by the sampled UE is the same as the Previous TAI in thecontext stored in the MME. That is, the MME can determine the TA visitedby the UE before the UE enters the current TA according to the Last TAIin the TAU Request message, and save the information about the TAvisited by the UE before the UE enters the current TA in the previousattaching or TAU procedure. For more details, see step S704. The MMElocates the record in Table 3 by using the Last TAI (or Previous TAI) asa source TA and using the Current TAI as a target TA. If no record isfound, the MME creates the record. If the record is found successfully,the MME modifies the count field in the record. As a way of modifyingthe count field, the MME may add 1 to the counter, or perform aweighting operation according to the property of the user of the UE,target TA, and time segment, namely, add a weighted value to theexisting count.

TABLE 3 Recent motion frequency (number of Target Percent times persecond, last Source TA TA Count Percent order 10 minutes) TA1 TA1 500  50% 1 10 TA1 TA2 50  5.0% 4 1.1 TA1 TA3 300 30.0% 2 5.7 TA1 TA4 15015.0% 3 3.5 TA3 TA1 700   35% 1 8.3 TA3 TA2 200   10% 4 3.0 TA3 TA3 65032.5% 2 5.1 TA3 TA5 450 22.5% 3 3.5

Table 3 is only an example. In practice, the content of the tabledepends on the actual needs. For example, “Count” does not necessarilycoexist with “Count after a scale factor is applied”.

The MME calculates and refreshes the percent of motions from a source TAto each target TA in real time or periodically, ranks the motionsaccording to the percent, and calculates the recent motion frequency.

In this embodiment, the MME needs only to track two consecutive TAUprocedures of the sampled UE, and obtain the information about themotion of the UE from the previous TA (identified by Previous TAI) tothe current TA (identified by Current TAI). Therefore, the MME clearsthe sampling flag in the UE context after processing the TAU Requestmessage of the sampled UE in the way above.

Step S703 occurs after step S702: When processing all received AttachRequest messages or TAU Request messages, the MME selects a certainproportion (such as 5%) of UEs as sampled UEs randomly. A sampling flagis affixed into the context of each sampled UE on the MME.

When the MME allocates the TA list, the MME needs to consider only thepercent of motions of the UE from a current TA to each target TA.Therefore, for different current TA, the percent of the UE beingselected as a sampled UE is not necessarily the same in the Attachprocedure or TAU procedure. For example, in a TA with dense population,the percent of the UE being selected as a sampled UE in an attachingprocedure or TAU procedure initiated in the TA may be low, for example,2%; in a TA with sparse population, the percent may be higher, forexample, 15%; when the MME is just started and few history records ofthe motion trace of the UE have been collected, the sampling percent maybe high; after the MME runs for a period and the history record includesenough data, the sampling percent may be low, for the purpose ofupdating the history data. In different time segments, the percent maydiffer. For example, in rush hours or time segments characterized bycrowds of traveling people or frequent TAU procedures, the percent maybe low.

Step S704: For the sampled UEs, the MME may record the Current TAIcarried in the Attach Request or TAU Request into the Previous TAI ofthe UE context, and add only the Current TAI into the TA list whenallocating the TA list to the sampled UE. The MME may allocate the TAlist to the sampled UE by sending an Attach Accept message or TAU Acceptmessage.

For the UE not sampled, according to the Current TAI carried in theAttach Request or TAU Request, the MME searches Table 3 to select thetarget TAs to which the UE will probably move from the current TA, addsthe selected target TAs and the current TA of the UE into the TA list,and allocates the TA list to the UE.

The selection conditions and the selection method in the firstembodiment are applicable to the third embodiment except the scalefactor. When the sampling-based method for collecting statistics isapplied, the TA list allocated to the sampled UE always includes onlythe TA currently visited by the sampled UE, and only the TAU initiatedby the sampled UE exerts impact on the data in Table 3. Therefore, thedata in Table 3 keeps stable no matter which TAs are included in the TAlist allocated to the UE. Therefore, the scale factor in the firstembodiment is not required here.

In the third embodiment, the MME tracks only the motion trace of thesampled UE in a TAU period, and obtains the statistic information aboutthe sampled UE moving from the previous TA to the next TA. In practice,the MME may keep tracking a sampled UE for several TAU periodscontinuously. In such periods, the TA list allocated by the MME to thesampled UE includes only the TA currently visited by the sampled UE. Inthis way, the MME obtains continuous trace of the sampled UE movingbetween the TAs, and obtains more precise statistic information.

For that purpose, a fourth embodiment is put forward. In the fourthembodiment, the MME keeps tracking the sampled UE for two TAU periodscontinuously, and obtains continuous motion trace of the sampled UEbetween three TAs. Specifically, the MME may add two fields “PreviousTAI” and “Previous2 TAP” into the context. The values of the two fieldsare initialized to invalid values. As shown in FIG. 8, the method in thefourth embodiment includes the following steps:

Step S801: The MME receives an Attach Request message or TAU Requestmessage. The Attach Request message or TAU Request message carries aCurrent TAI. The TAU Request message further carries a Last TAI.

Step S802: If a TAU procedure is initiated by the UE, the MME judgeswhether a sampling flag is set in the context of the UE. If a samplingflag is set in the UE context, and the Previous2 TAI and the PreviousTAI in the context are set to valid TAI values, the MME locates thecorresponding record in Table 4 by using the Previous2 TAI as a sourceTA, using the Previous TAI as an intermediate TA (the value of theintermediate TA may also be obtained from the Last TAI in the TAURequest message), and using the Current TAI in the Attach Requestmessage or TAU Request message as a target TA. If no record is found,the MME creates the record; if the record is found successfully, the MMEmodifies the count field in the record. As a way of modifying the countfield, the MME may add 1 to the counter, or perform a weightingoperation according to the property of the user of the UE, target TA,and time segment, namely, add a weighted value to the existing count.

TABLE 4 Recent motion frequency Inter- Tar- (number of times Sourcemediate get Percent per second, last TA TA TA Count Percent order 10minutes) TA1 TA2 TA1 10 NA*1 NA 0.5 TA1 TA2 TA2 40 NA*2 NA 2.1 TA1 TA2TA3 850 93.4%  1 10 TA1 TA2 TA4 100  6.6% 2 5.7 TA3 TA2 TA2 100 NA*2 NA2.5 TA3 TA2 TA1 1400 100% 1 15.4 TA2 TA3 TA3 300 NA*2 NA 6.4 TA2 TA3 TA5700 100% 1 12.5 *1In this record, because the recent motion frequency islower than the threshold, it is excluded from the factors forcalculating and ranking the percents in this embodiment. *2In thisembodiment, the records whose target TA is the current TA are notinvolved in calculating or ranking the percents.

Table 4 is only an example. In practice, the content of the tabledepends on the actual needs. For example, “Count” does not necessarilycoexist with “Count after a scale factor is applied”.

The MME calculates and refreshes the percent of motions to each targetTA in real time or periodically after the UE moves from a source TA toan intermediate TA, ranks the motions according to the percent, andcalculates the recent motion frequency.

If the Previou2 TAI of the UE is valid, namely, if a complete continuoustracking procedure (two TAU periods) is finished for the UE, the MMEclears the sampling flag in the UE context, and sets the Previous TAIand the Previous2 TAI to an invalid value. If the Previou2 TAI of the UEis invalid, the MME sets the Previous2 TAI to the value of Previous TAI,and then sets the Previous TAI to the value of the Current TAI carriedin the TAU Request message.

Step S803 occurs after step S802: When processing all received AttachRequest messages or TAU Request messages, if the UE is not set as asampled UE, the MME selects a certain proportion (such as 5%) of UEs assampled UEs randomly. A sampling flag is affixed into the context ofeach sampled UE on the MME.

For the UEs located in different current TAs, the selected proportion ofthe UEs may vary.

Step S804: For the sampled UEs, including the sampled UEs which have notundergone a complete continuous tracking procedure, the MME may recordthe Current TAI carried in the Attach Request or TAU Request into thePrevious TAI of the UE context, and add only the Current TAI into the TAlist when allocating a TA list to the sampled UE. The MME may allocatethe TA list to the sampled UE by sending an Attach Accept message or TAUAccept message.

For the UE not sampled, the MME searches Table 4 to select the targetTAs to which the UE will probably move after the UE moves from thesource TA to the intermediate TA, where the source TA is the TAidentified by the Last TAI carried in the Attach Request or TAU Request(for the Attach Request message, the Current TAI may be a Last TAIconcurrently), and the intermediate TA is the TA identified by theCurrent TAI; and then the MME adds the selected target TAs and thecurrent TA of the UE into the TA list, and allocates the TA list to theUE.

In the fourth embodiment, the MME tracks the motion of the UE betweenthe TAs by using only the Current TAI carried in the Attach Requestmessage or TAU Request message. Therefore, after a UE is selected as asampled UE, the MME needs to track the UE for two more continuous TAUperiods to obtain the motion trace of the UE from the source TA to theintermediate TA and to the target TA. In fact, the TAU Request messagecarries a Last TAI in addition to the Current TAI. If the Last TAI isconsidered additionally, the MME can track the UE for only one TAUperiod after the UE is selected as a sampled UE, thus accomplishing theeffect of the fourth embodiment.

For that purpose, a fifth embodiment is put forward. Specifically, theMME still adds two fields “Previous TAI” and “Previous2 TAI” into thecontext of the UE. The values of the two fields are initialized toinvalid values. As shown in FIG. 9, the method in the fifth embodimentincludes the following steps:

Step S901: The MME receives an Attach Request message or TAU Requestmessage. The Attach Request message or TAU Request message carries aCurrent TAI. The TAU Request message further carries a Last TAI.

Step S902: If a TAU procedure is initiated by the UE, the MME judgeswhether a sampling flag is set in the context of the UE. If so, thePrevious2 TAI (including the Previous TAI) in the context should be avalid TAI. The MME locates the corresponding record in Table 4 by usingthe Previous2 TAI as a source TA, using the Previous TAI as anintermediate TA, and using the Current TAI in the TAU Request message asa target TA. If no record is found, the MME creates the record. If therecord is found successfully, the MME modifies the count field in therecord. As a way of modifying the count field, the MME may add 1 to thecounter, or perform a weighting operation according to the property ofthe user of the UE, target TA, and time segment, namely, add a weightedvalue to the existing count.

The MME calculates and refreshes the percent of motions to each targetTA in real time or periodically after the UE moves from a source TA toan intermediate TA, ranks the motions according to the percent, andcalculates the recent motion frequency.

Now, a complete continuous tracking procedure (1 TAU period) is finishedfor the sampled UE, and the MME clears the sampling flag in the contextof the UE.

Step S903 occurs after step S902: When processing all received TAURequest messages, the MME selects a certain proportion (such as 5%) ofUEs as sampled UEs randomly. A sampling flag is affixed into the contextof each sampled UE on the MME.

Step S904: For the sampled UEs, the MME may record the Current TAIcarried in the TAU Request message into the Previous TAI of the contextof the UEs, record the Last TAI carried in the TAU Request message intothe Previous2 TAI of the context, and add only the current TA into theTA list when allocating the TA list to the sampled UE. The MME mayallocate the TA list to the sampled UE by sending an Attach Acceptmessage or TAU Accept message.

For the UEs which send an Attach Request message and the UEs notsampled, the MME searches Table 4 to select the target TAs to which theUE will probably move after the UE moves from the source TA to theintermediate TA, where the source TA is the TA identified by the LastTAI carried in the Attach Request or TAU Request (for the AttachRequest, the Current TAI may be a Last TAI concurrently), and theintermediate TA is the TA identified by the Current TAI; and then theMME adds the selected target TAs and the current TA of the UE into theTA list, and allocates the TA list to the UE.

It should be noted that the embodiments of the present invention are notonly applicable to the EPS, but also applicable to other networkenvironments. When the embodiments of the present invention are appliedto a Circuit Switched (CS) domain environment of the communicationsystem, the MME in the foregoing embodiments is equivalent to a MobileSwitching Center (MSC) in the CS domain, and the basic paging area is aLocation Area (LA) in the WCDMA system. When the embodiments of thepresent invention are applied to a GPRS/UMTS system, the MME in theforegoing embodiments is equivalent to a Serving GPRS Supporting Node(SGSN) in the GPRS/UMTS, and the basic paging area is a Routing Area(RA) in the Packet Switched (PS) domain of the WCDMA system. When theembodiments of the present invention are applied to a WorldInteroperability for Microwave Access (WiMax) system, the MME in theforegoing embodiments is equivalent to an Access Serving Node Gateway(ASN-GW) in the WiMax system, and the basic paging area is a paging areain the WiMax system.

Persons of ordinary skill in the art should understand that all or partof the steps of the method under the present invention may beimplemented by a program instructing relevant hardware. The program maybe stored in a computer readable storage medium. When the program runs,the steps of the method specified in any of the embodiments above can beperformed. The storage medium may be a magnetic disk, CD-ROM, Read-OnlyMemory (ROM), or Random Access Memory (RAM).

Although the invention is described through some exemplary embodiments,the invention is not limited to such embodiments. It is apparent thatthose skilled in the art can make modifications and variations to theinvention without departing from the spirit and scope of the invention.The invention is intended to cover the modifications and variationsprovided that they fall in the scope of protection defined by thefollowing claims or their equivalents.

What is claimed is:
 1. A method for allocating a paging area for a UserEquipment (UE) in a wireless communication system, comprising:determining a first basic paging area currently visited by a first UE inthe wireless communication system, wherein the first basic paging areadefines a wireless coverage area; and allocating a paging area to thefirst UE according to a history record that defines a motion trace of aplurality of UEs that are located in the first basic paging area,wherein the paging area comprises a plurality of basic paging areasidentified in the history record.
 2. The method according to claim 1,wherein the determining the first basic paging area currently visited bythe first UE comprises: receiving an identifier (ID) of the first basicpaging area from the first UE or a Radio Access Network (RAN).
 3. Theaccording to claim 1, wherein: the history record comprises informationindicating times of the plurality of UEs in the first basic paging areamoving to other basic paging areas in each unit of time within aspecific period.
 4. The method according to claim 1, wherein: thehistory record comprises: actual number of motions of the plurality ofUEs from the first basic paging area currently visited by the first UEto basic paging areas adjacent to the first basic paging area, or aresult obtained after a scale factor is applied to the actual number ofmotions.
 5. The method according to claim 4, wherein: if the scalefactor is less than 1, the actual number of motions corresponding to theadjacent basic paging areas inside the paging area allocated to theplurality of UEs is divided by the scale factor, or the actual number ofmotions corresponding to the adjacent basic paging areas outside thepaging areas allocated to the plurality of UEs located in first basicpaging area is multiplied by the scale factor.
 6. The method accordingto claim 1, wherein: the plurality of basic paging areas identified inthe history record comprise multiple continuous adjacent basic pagingareas, and the multiple continuous adjacent basic paging areas are aresult of prediction performed according to the history record.
 7. Themethod according to claim 6, wherein: the number of multiple continuousbasic paging areas depends on at least one of user type, property ofbasic paging area, time segment, and motion speed of the first UE. 8.The method according to claim 1, wherein the plurality of basic pagingareas identified in the history record comprise basic paging areasvisited by the plurality of UEs before the plurality of UEs enter intothe first basic paging area, and basic paging areas visited by theplurality of UEs after the plurality of UEs left the first basic pagingarea.
 9. The method according to claim 1, wherein the plurality of UEsinclude the first UE.
 10. The method according to claim 9, wherein theplurality of basic paging areas identified in the history record includethe first basic paging area.
 11. The method according to claim 1,wherein the first basic paging area and the plurality of basic pagingareas are tracking areas in an Evolved Packet System (EPS).
 12. Themethod according to claim 11, wherein the method is performed by aMobility Management Entity (MME) in the EPS.
 13. An apparatus forallocating a paging area for a User Equipment (UE) in a wirelesscommunication network, comprising: a processor; and a memory coupled tothe processor and having computer executable instructions which, whenexecuted by the processor, cause the processor to: determine a firstbasic paging area currently visited by a first UE in the wirelesscommunication network, wherein the first paging area defines a wirelesscoverage area; and allocating a paging area to the first UE according toa history record that defines a motion trace of a plurality of UEs thatare located in the first paging area, wherein the paging area comprisesa plurality of basic paging areas identified in the history record. 14.The apparatus according to claim 13, wherein the plurality of basicpaging areas identified in the history record comprise basic pagingareas visited by the plurality of UEs before the plurality of UEs enterinto the first basic paging area, and basic paging areas visited by theplurality of UEs after the plurality of UEs left the first basic pagingarea.
 15. The apparatus according to claim 13, wherein the plurality ofUEs include the first UE.
 16. The apparatus according to claim 15,wherein the plurality of basic paging areas identified in the historyrecord include the first basic paging area.
 17. The apparatus accordingto claim 13, wherein the first basic paging area and the plurality ofbasic paging areas are tracking areas in an Evolved Packet System (EPS).18. The apparatus according to claim 17, wherein the apparatus is aMobility Management Entity (MME) in the EPS.